Field
This document relates to a stereoscopic image display device and a method of controlling a backlight thereof.
Related Art
Image display devices are classified into a stereoscopic technique and an autostereoscopic technique.
The stereoscopic technique uses binocular parallax images which are great in the stereoscopic effect, and may have a type of using glasses and a type of not using glasses. In the type of using glasses, binocular parallax images are displayed on a direct view display panel or a projector by changing polarization directions or in the temporal division manner, and polarization glasses or liquid crystal shutter glasses are used to implement stereoscopic images. In the type of not using glasses, the stereoscopic images are implemented by dividing optical axes of binocular parallax images, by using optical plates such as parallax barriers provided at front and rear surfaces of a display panel.
FIG. 1 is a schematic diagram illustrating an stereoscopic image display device of the glass type using shutter glasses. A black part of the shutter glasses is a closed shutter for blocking light directing toward a viewer and a white part thereof is an opened shutter for transmitting light directing toward the viewer. In FIG. 1, if a liquid crystal display is selected as a display device DIS, a backlight unit (BLU) providing light to the display device DIS is necessary.
Referring to FIG. 1, the left eye shutter STL of the shutter glasses ST is opened when left eye data RGBL is addressed in the display device DIS. The right eye shutter STR is opened when right eye image data RGBR is addressed in the display device DIS. Therefore, the viewer sees only the left eye image with the left eye and sees only the right eye image with the right eye, thereby obtaining a three-dimensional effect by a parallax.
The liquid crystal display may include an over-driving logic circuit used to compensate the response speed of liquid crystal. The over-driving logic circuit increases a pixel data value for a current frame to a higher value if a pixel data value of an input image becomes larger in the current frame than in a previous frame, whereas it decreases a pixel data value for a current frame to a lower value if a pixel data value of the input image becomes smaller in the current frame than in a previous frame, thereby adjusting data voltages applied to liquid crystal cells to compensate a slow response characteristic of the liquid crystal. The over-driving logic circuit may be implemented by a look-up table where pixel data for previous and current frames of an input image is input and corresponding pre-stored modulation values are output. FIGS. 2A and 2B show an example of the over-driving method. If a pixel data value is increased from ‘127’ to ‘191’ as shown in FIG. 2A, the over-driving logic circuit increases the value ‘191’ to a value ‘223’ higher than that as shown in FIG. 2B. In addition, if the pixel data value is decreased from ‘191’ to ‘63’ as shown in FIG. 2A, the over-driving logic circuit decreases the value ‘63’ to a value ‘31’ lower than that as shown in FIG. 2B.
In the stereoscopic image display device, it is possible to improve an image tailing by reducing a 3D crosstalk and a motion blurring through a BDI (black data insertion). In this method, as shown in FIG. 3, during a (n+1)-th (where n is a positive integer) frame period Fn+1, left eye (or right eye) image data is addressed in the display panel, during a (n+2)-th frame period Fn+2, black data having nothing to do with an input image is addressed in the display panel, and thereafter, during a (n+3)-th frame period Fn+3, right eye (or left eye) image data is addressed in the display panel. According to this method, the frame previous to the left eye image data frame and the right eye image data frame is a reset frame used to address black data, and thus it is difficult to improve the 3D crosstalk when the over-driving logic circuit used in the 2D image driving method in the related art is used in the 3D image display as it is. The 3D crosstalk means a degree that a left eye image and a right eye image overlap each other on one eye (the left eye or the right eye) of a user, and is defined by a ratio of black grayscale brightness to white grayscale brightness of one eye image. For example, when target brightness to be reached during the (n+1)-th frame period Fn+1, target brightness to be reached during the (n+2)-th frame period Fn+2, and target brightness to be reached during the (n+3)-th frame period Fn+3 are “180,” “0,” and “150,” (as shown in the left part of FIG. 3) respectively, and “255,” “0,” and “150” (as shown in the right part of FIG. 3), respectively, the brightness is measured to be different during the (n+3)-th frame period Fn+3 although pixel data with the same grayscale value is addressed in the same pixels of the display device. This is because, as shown in the right part of FIG. 3, when the target brightness to be reached during the (n+1)-th frame period Fn+1 is “255”, the brightness during the (n+2)-th frame period Fn+2 is increased to the brightness Di higher than the target brightness for the black grayscale data due to the response delay of the liquid crystal. As a result, as shown in the right part of FIG. 3, the brightness during the (n+3)-th frame period Fn+3 becomes higher than the target brightness of 150.